56 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
has been patent to nearly all writers. Perhaps the most novel conjec- 
ture as to their function is that recently advanced by Karpinsky,! who, 
as an alternative hypothesis to regarding them as caudal spines, refers 
the thrice-coiled spiral of Helicoprion to the snout region, and supposes 
it to have been a powerful weapon for attack and defence, each 
individual possessing but a single organ of this kind (ef. text-figure 1). 
The Russian Director’s main reason for excluding these spirals from the 
mouth cavity, namely on account of their large size (26 cm. in diameter), 
is not, in the opinion of at least two of his critics, an insurmountable 
objection, nor can any argument for an external position be based on the 
presence of so-called “ placoid scales” over and around the bases of the 
segments or teeth, when it is 
evident from the author’s 
beautiful figures that he has 
mistaken calcified cartilage 
for shagreen granules. 
In the reviews which have 
appeared of Dr. Karpinsky’s 
memoir,” it is admitted that 
much evidence has _ been 
brought forward in favor of 
Karpinsky’s conjectural restoration of Helt- the yiew that Edestus and 
coprion bessonowi, from the Russian Permo- 
Carboniferous (after Karpinsky). X 7p. 
Helicoprion should be looked 
upon as Paleozoic sharks 
with sharp piercing teeth, which were never shed, but became fused 
into whorls as the animal grew. And quite recently it has been 
claimed by the present writer * that positive proof of the odontological 
nature of Edestus, Campyloprion, and Helicoprion is furnished by com- 
parison with the dental armature of Campodus. According to this view, 
the curved or coiled “spines”? of Edestus and Helicoprion are not der- 
mal defences at all, but veritable teeth corresponding to the symphysial 
series of Protodus, Campodus, the existing Cestracion, Carcharias, 
Chlamydoselache and other forms, only more modified with respect to 
curvature. Initial stages in the coiling of symphysial or intermandibular 
1 Karpinsky, A., Ueber die Reste von Edestiden, und die neue Gattung Heli- 
coprion. Verhandl. k. russ. Mineral. Ges. St. Petersburg, Vol. XXXVI., p. 467, 
1899. 
2 Woodward, A. S., Helicoprion, — Spine or Tooth? Geol. Mag. (4), Vol. VIL, p. 
33, 1900. — Eastman, C. R., Karpinsky’s Genus Helicoprion: a Review. Amer. 
Nat., Vol. XXXIV., p. 579, 1900. 
8 Science, n.s., Vol. XIV. (1901), p. 795. — Geol. Mag. (4), Vol. IX. (1902), p. 148. 
